In recent years, high efficiency electric motors have become desirable to meet the challenges of providing power without the usage of fossil fuel sources, for example in hybrid and electric vehicles. Interior permanent magnet (IPM) motors have become popular due to their high efficiency performance, as an IPM is an increasingly efficient synchronous motor due to advances in high-energy permanent magnet technology, smart inverters, and digital controllers.
IPM electric machines have magnets built into the interior of the rotor, and each magnetic pole on the rotor is conventionally created by putting permanent magnet material into slots formed in the laminated stack of the rotor. Such slots are typically not completely filled with magnetic material, instead being designed to hold a magnet in the center with voids at two opposite ends of the slot. The rotor is rotatable within a stator which includes multiple windings to produce a rotating magnetic field in the frame of reference of the stator.